The impact of cranioplasty on neurological function

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complications including subdural effusion, cortical hernia- tion, hydrocephalus infection and on rare occasions, sudden death. 13 – 16. One complication that ...
British Journal of Neurosurgery, October 2013; 27(5): 636–641 © 2013 The Neurosurgical Foundation ISSN: 0268-8697 print / ISSN 1360-046X online DOI: 10.3109/02688697.2013.817532

ORIGINAL ARTICLE

The impact of cranioplasty on neurological function Stephen Honeybul1, Courtney Janzen2, Kate Kruger2 & Kwok M. Ho3 1Department of Neurosurgery, Sir Charles Gairdner Hospital and Royal Perth Hospital, Perth, Western Australia, Australia, 2Department of Occupational Therapy, Sir Charles Gairdner Hospital, Perth, Western Australia, Australia, and 3Department

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of Intensive Care Medicine, Royal Perth Hospital and School of Population Health, University of Western Australia, Western Australia, Australia

complications including subdural effusion, cortical herniation, hydrocephalus infection and on rare occasions, sudden death.13–16 One complication that has received relatively little attention is the neurological dysfunction that can occur due to the absence of the bone flap and the subsequent distortion of the brain under the scalp as cerebral oedema subsides and the unprotected brain is exposed to atmospheric pressure. The classical descriptions of this phenomenon are of an initial period of improvement after the decompressive surgery followed by a period of neurological deterioration. Thereafter the diagnosis is confirmed when the symptoms resolve or improve following replacement of the bone flap. Syndrome of the trephined refers to the symptoms of headache, seizures, mood swings and behavioural disturbance, and was first described by Grant and Norcross in 1939.17 The term syndrome of the sinking scalp flap was introduced by Yamaura and Makino18 and this describes the objective neurological deficits that can occur in patients with a skull bone defect. Both conditions are thought to be rare; however, recent studies have described significant physiological and clinical changes that can occur after cranioplasty and it is possible that subtle but important neurocognitive improvement is more common after cranioplasty than previously appreciated.19–25 The aim of this study was to formally assess whether cranioplasty is associated with a significant improvement in functional and neurocognitive function in a cohort of patients with mixed underlying pathology.

Abstract Objectives. To assess changes in neurological function after cranioplasty. Methods. Functional and neurocognitive assessments including activities of daily living assessment, functional independence measure (FIM) and the Cognitive assessment report (COGNISTAT) were conducted on all patients within 72 h before and 7 days after cranioplasty. A change in the total FIM score of 2 points was taken to be clinically significant. Results. Assessments were performed on 25 patients. The functional status was unchanged in eighteen patients (72%), four patients (16%) demonstrated a significant improvement and three patients (12%) deteriorated significantly. Those with deterioration after cranioplasty had some forms of complications including pneumocephalus or seizure. After excluding the three patients who had immediate medical or surgical complications after surgery, there was a mild overall improvement in the mean FIM score (2.1, 95% confidence interval 0.1–4.3, p ⴝ 0.049), mainly due to an improvement in their motor function. Conclusions. A small but significant number of patients appear to improve clinically following cranioplasty. The so-called syndrome of the trephined may be more common than had been previously appreciated. Keywords: cranioplasty; decompressive craniectomy; syndrome of trephined; traumatic brain injury

Introduction Over the past 2 decades there has been a resurgence of interest in the use of decompressive craniectomy not only in the context of traumatic brain injury1,2 and stroke,3,4 but also more recently following subarachnoid haemorrhage,5,6 severe intracranial infection,7,8 dural sinus thrombosis9,10 and inflammatory conditions.11,12 The procedure itself is technically straightforward; however, it is becoming increasingly apparent that both the initial craniectomy and the subsequent cranioplasty are associated with a number of

Method After obtaining hospital research ethical committee of Sir Charles Gairdner Hospital’s approval, all patients who underwent cranioplasty, between June 2010 and February 2013, had a pre-operative (⬍ 72 h) and post-operative functional and neurocognitive assessments (⬍ 7 days). These

Correspondence: Mr. Stephen Honeybul FRCS (SN) FRACS, Department of Neurosurgery, Sir Charles Gairdner Hospital and Royal Perth Hospital, Perth, Western Australia, Australia. Fax: ⫹ 08 9346 3824. E-mail: [email protected] Received for Publication 24 March 2013; accepted 16 June 2013

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The impact of cranioplasty 637 Table I. Characteristics of the patients included in the study (n ⫽ 25). Number (%) unless stated Variable otherwise

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were performed by two of the research team who had formal training in administering the assessments (CJ and KK). The data were then collated and analysed (KH and SH). The time period cut-off for the assessments was less than 3 days before and 7 days after the cranioplasty procedure. Timing of the cranioplasty relative to the initial craniectomy procedure was based on individual surgeons’ preferences, but in general at this institution a cranioplasty is performed once the patient is medically stable, there are no signs of infection and the scalp flap has sunk sufficiently such that the bone flap or reconstructive material can be safely inserted. The assessments were as follows:

Median age (IQR), years Male Mechanism of injury leading to craniectomy –Trauma –Stroke or intracranial hemorrhage –Infection Site of craniectomy –Bifrontal –Unilateral on the right –Unilateral on the left Time between craniectomy and cranioplasty, days (IQR, SD) Material used for cranioplasty –Autologous bone graft –Titanium plate Immediate complications after cranioplasty –Seizure –Pneumocephalus Mean functional independence measure (IQR) –Before cranioplasty –After cranioplasty Mean cognitive assessment score (IQR) –Before cranioplasty –After cranioplasty

1. Activities of daily living assessment and functional independence measure (FIM)26: The FIM instrument is a basic indicator of severity of disability and comprises 18 items, each of which is assessed against a seven point ordinal scale. The higher the score for an item, the more independently the patient is able to perform that task. Total scores range from 18 to 126. The items are divided into two major groups. The motor items, of which there are 13, and the cognitive items, of which there are 5. The rating scale designates major graduations in behaviour from dependence which is scored as 1 to independence for that task which is scored as 7.27 2. Cognitive assessment report (Cognistat): Cognistat, formerly known as the Neurobehavioral Cognitive Status Examination (NCSE), is a cognitive screening test that assesses five cognitive ability areas (language, construction, memory, calculations and reasoning). The test is useful in the acute setting because it is sensitive and, at the same time, can be easily and quickly administered.28,29

No.

Pathology

Type

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

51/M 40/M 16/M 59/M 58/M 37/F 67/F 22/M 19/M 67/F 40/M 26/M 30/M 53/F 70/M 64/F 40/M 23/F 35/M 68/M 16/M 19/M 35/M 56/M 44/M

TBI TBI TBI TBI Tumour ICH TBI TBI TBI SAH TBI TBI TBI TBI TBI Stroke SAH TBI TBI TBI TBI TBI TBI TBI Stroke

Unilateral (L) Bifrontal Bifrontal Bifrontal Bifrontal Unilateral (R) Unilateral (L) Unilateral (L) Unilateral (L) Unilateral (R) Unilateral (L) Unilateral (R) Unilateral (L) Bifrontal Unilateral (L) Unilateral (R) Bifrontal Unilateral (R) Bifrontal Unilateral (R) Bifrontal Bifrontal Bifrontal Unilateral (R) Unilateral (R)

19 (76) 5 (20) 1 (4) 10 (40) 8 (32) 7 (28) 100 (67–132, 128) 16 (64) 9 (36) 1 (4) 1 (4) 91.4 (58.0–124.5) 92.1 (66.5–126.0) 26.9 (22.5–35.0) 27.4 (23.0–35.0)

IQR: interquartile range; SD: Standard deviation.

The scores for both assessments were calculated and then compared before and after surgery.

Statistical analysis The characteristics of the patients are described as number and percentage and continuous variables are presented as mean or median with interquartile range (IQR). Changes in FIM and Cognistat before and after cranioplasty were compared using a paired t-test. A change in the total FIM of greater than 2 points was considered as clinically important.

Table II. Individual pre-operative and post-operative FIM scores (n = 25). Motor total subtotal Age/ Sex

40 (25–59) 19 (76)

Cognitive subtotal

Material

Preoperative

Postoperative

Preoperative

Titanium Titanium Autologous Titanium Titanium Autologous Autologous Autologous Titanium Autologous Autologous Autologous Autologous Autologous Titanium Autologous Autologous Titanium Titanium Titanium Autologous Autologous Autologous Autologous Autologous

60 13 88 13 52 40 46 91 91 39 89 91 34 89 82 32 91 13 91 75 91 91 91 74 34

61 13 88 13 58 46 54 91 91 43 89 91 34 91 82 32 91 13 91 47 91 91 91 74 34

19 13 35 11 27 31 18 35 32 26 31 34 11 35 26 30 28 5 35 35 32 35 35 31 27

Total FIM score

PostPrePostoperative operative operative Change 19 10 35 6 30 33 20 35 32 28 31 35 11 35 26 30 28 5 35 35 32 35 35 31 27

79 26 123 24 126 71 54 126 123 65 120 125 28 124 108 62 119 18 126 110 123 126 126 105 51

80 23 123 19 135 79 74 126 123 71 120 126 28 126 108 62 119 18 126 82 123 126 126 105 51

1 ⫺3 0 ⫺5 9 8 20 0 0 6 0 1 0 2 0 0 0 0 0 ⫺ 28 0 0 0 0 0

Outcome Same Worse Same Worse Improved Improved Improved Same Same Improved Same Same Same Same Same Same Same Same Same Worse Same Same Same Same Same

TBI: Traumatic brain injury; ICH: Intracerebral haemorrhage; SAH: Subarachnoid haemorrhage; Outcome: an improvement of more than 2 points on the FIM total was deemed clinically significant.

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S. Honeybul et al. Table III. Pre-operative and post-operative COGNISTAT scores of those patients that improved following cranioplasty. Patient No. 5 Patient No. 6 Patient No. 7 Patient No. 10

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Pre Consciousness Orientation Attention Repetition Language Comprehension Repetition Naming Construction Memory Calculations Reasoning Similarities/Judgement Total score (excl Repetition) Percentage improvement

Post

Alert Alert 12 12 8 8 1 1 6 6 12 12 12 12 8 8 6 6 4 12 0 1 6 6 4 5 66 76 15.20%

Pre Alert 10 8 2 6 12 12 8 4 9 4 8 3 72

Post Alert 12 8 1 6 12 12 8 6 12 4 8 3 79 9.70%

Pre

Post

Alert 4 4 2 2 4 4 3 3 4 2 2 2 32

Alert 6 6 2 4 6 6 3 3 8 2 2 4 46 37%

Pre

Post

Alert Alert 4 7 6 7 2 1 5 6 12 12 12 12 7 8 0 0 9 11 1 3 4 6 3 3 53 63 18.90%

N. B. The repetition score was not included in the total score because a greater number of attempts does not signify improvement.

Results Of the 27 patients who had a cranioplasty during the study period, 25 were recruited into the study. Two patients were not recruited because FIM and Cognistat assessments could be performed within the study timeframe before and after surgery due to logistical difficulties. The median time between craniectomy and cranioplasty was 100 days (IQR 67–132). The overall characteristics of the 25 patients on whom pre-operative and post-operative assessments were administered are shown in Table I. The individual results of the FIM assessments are shown in Table II. Using an increase in the total FIM score of 2 points as a cut-point, 18 patients (72%) had no significant functional improvement and 4 patients (16%) had significant functional improvement within 7 days of cranioplasty. There was no particular pattern discernable; however, most of the changes appeared to be in motor function. Patient No. 7 demonstrated the greatest improvement and could stand unaided for the first time 2 days following her cranioplasty. The four patients listed in Table III also showed some improvements in COGNISTAT scores and improvement in memory appeared to be a consistent finding. Three patients significantly deteriorated following cranioplasty. Patient No. 2 had poor neurological function pre-operatively, however was able to follow some simple commands and to communicate. Post-operatively he sustained a number of seizures and although he regained his former level of function there was a temporary deterioration at the time of neurocognitive assessment. Patient No. 20 Table IV. A lack of association between neurological improvement or deterioration and timing of cranioplasty after craniectomy. Neurological changes after cranioplasty Improved (n ⫽ 4)

Deteriorated (n ⫽ 3)

Timing of cranioplasty in days 3 (12) ⬍ 90 1 (4) ⬎ 90 3 (12) ⬍ 180 1 (4) ⬎ 180

2 (8) 1 (4) 2 (8) 1 (4)

Values inside parenthesis are percentage.

No change (n ⫽ 22) 5 (20) 13 (52) 17 (68) 1 (4)

P value 0.132 0.267

had an exacerbation of pre-existing vertigo following his cranioplasty and although cognitive function was retained he lost considerable motor function for approximately 1 week. Patient No. 4 exhibited the almost classical features of syndrome of the trephined; however, there was a temporary deterioration following his cranioplasty and this is documented as an illustrative case. After excluding these three patients who had immediate surgical or medical complications from cranioplasty, there was a mild overall improvement in the mean FIM score (2.1, 95% confidence interval 0.1–4.3, p ⫽ 0.049) for the remaining 22 patients. Using cut-points of 90 and 180 days between craniectomy and cranioplasty as cut-points, timing of cranioplasty appeared to have no significant association with whether neurological improvement or deterioration would occur (Table IV).

Illustrative clinical case Patient No. 4 was a previously fit and well fiftynineyearold male who fell approximately 3 m from a ladder and sustained an isolated closed head injury. On initial presentation his Glasgow Coma Score was 13 (E3, M6, V4). He was drowsy and confused but readily obeyed commands. Initial scan revealed a shallow left-sided acute subdural haematoma and bifrontal contusions (Fig. 1). He was admitted to the neurosurgical ward and kept under close observation. Over the following 9 days his clinical condition improved and consideration was given to discharging him home. On day 10 he became progressively more drowsy and a repeat CT scan showed evolution of the contusions with mass effect and midline shift (Fig. 2). As a consequence of these findings he was intubated, ventilated and transferred to the intensive care where an intracranial pressure (ICP) monitor was inserted. Over the following 24 h he developed intractable intracranial hypertension with an ICP consistently above 30 mmHg, despite the insertion of an external ventricular drain and maximal medical management. In view of these developments he went on to have a bifrontal decompressive craniectomy and he subsequently made a good recovery. Six weeks following surgery he was involved actively in rehabilitation and was able to stand unaided and walk a few steps.

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The impact of cranioplasty 639

Fig. 1. Initial axial non contrast CT scan showing an acute left sided subdural haematoma and bifrontal contusions.

He could feed himself but was mildly confused. There was then a slow but steady deterioration such that he became completely dependant and communication was limited to a few mumbled words. CT scan confirmed considerable sinking of the scalp flap and it was felt that this may be the cause of the neurological deterioration. Unfortunately following an uneventful cranioplasty procedure there was a further deterioration such that his FIM score dropped from 24 to 19. Post-operative CT scan confirmed considerable pneumocephalus and it was felt that this was a contributory factor (Fig. 3). Over a 10-day period he slowly improved and was discharged back to rehabilitation. He then made a rapid and dramatic recovery. He was discharged home after 1 month fully independent and on review 2 months later (3 months following the cranioplasty and approximately 6 months following the initial injury) he was considering a return to work on a part-time basis.

Discussion Whilst the primary function of a cranioplasty procedure is to provide protection to the underlying brain and restore cosmesis, it is becoming increasingly apparent that it can lead to

significant changes in cerebrovascular and cerebrospinal fluid (CSF) hydrodynamics.24,30–33 The effect that these changes have on clinical function has yet to be established; however, a number of reports have documented changes in neurological function following restoration of cranial coverage.19,20,22,23,34,35 Until now most of these studies have taken the form of retrospective case reports which would imply that this is relatively rare observation; however, the results of this prospective study suggest that clinical improvement following cranioplasty may be more common than has previously been appreciated. Overall there was some degree of clinical recovery in four of the 25 patients which would indicate that within this cohort there was a 16% incidence of some degree of neurological improvement. This may however be an underestimation because the improvement noted in the Patient No. 4 who seemed to demonstrate the classical symptoms of syndrome of the trephined fell outside the predetermined assessment period. This case serves to highlight the methodological limitations of assessing patients within a relatively narrow time period post-operatively; however, a relatively small fixed time period is required so as not to confuse a clinical improvement due to cranioplasty with the normal recovery from the initial pathological insult.

Fig. 2. Axial non contrast CT scan at day 10. Maturation of the contusions with local mass effect and midline shift.

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S. Honeybul et al. derive maximal benefit because of either clinical deterioration or failure to progress. A final consideration is perhaps not why patients improve following restoration of cranial coverage, but why most patients seem to tolerate considerable sinking of the scalp with obvious distortion of the cortical surface. Whether this relates to CSF hydrodynamics or cerebral metabolism remains to be established but this would be an interesting focus of future research.

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Declaration of interest: The authors report no declarations of interest. The authors alone are responsible for the content and writing of the paper.

References

Fig. 3. Pneumocephalus following titanium cranioplasty. (N. B. patients are participating in a clinical trial comparing titanium versus autologous bone cranioplasty. Available at http://www.anzctr.org.au).

Indeed, clinical recovery can occur for many months following traumatic brain injury and even when using the relatively broad categories of the Glasgow outcome scale, ongoing recovery has been documented up to 18 months following decompressive craniectomy.36 In view of these observations, further work will be required to optimise the timing, accuracy and utility of the pre-existing neurocognitive assessments. The results of this study have raised more questions that it can answer. In the first instance the underlying pathophysiology responsible for the changes in neurological function after cranioplasty remains to be established. Several mechanisms have been proposed including the direct effects of atmospheric air on the brain,25 alterations in CSF dynamics, changes in cerebral blood flow24 and altered cerebral metabolism.33 It may be that no single mechanism is responsible and the hypothesis that the aetiology is multifactorial would be supported by the observation that there was no consistent pattern of neurological change for those patients that did improve following cranioplasty. A more detailed neurocognitive assessment or functional imaging may provide more definitive information although completing these assessments within such a narrow timeframe especially in patients who have recently undergone surgery, may be difficult. A second consideration is the need to recognise those patients that are most susceptible to neurological deterioration due to the absence of a bone flap or those who are most likely to improve after cranioplasty. This will enable early referral back to the neurosurgical service for consideration of an early cranioplasty and will minimise delays in rehabilitation and prevent commencing unnecessary treatments such as anti-depression that may not be necessary. It will also prevent important and often scarce rehabilitation resources being unnecessarily apportioned to patients who cannot

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